1. Field of the Invention
This invention relates to an ultrahigh strength and ultralow elastic modulus titanium alloy showing linear elastic deformation behavior, wherein the structure of the titanium alloy is beta. Compared with conventional titanium alloys having similar properties and applications, the strength of the titanium alloy is so high that it is more than 1150 megapascal (MPa) and the elastic modulus is so low that it is less than 60 gigapascal (GPa).
2. Description of the Related Art
A titanium alloy is a representative lightweight metal. Because of its high specific strength and excellent corrosion resistance, it may be utilized in a variety of applications, such as aerospace industry, chemical engineering field, use as an in vivo implant material, sports equipment, and so on. Such a titanium alloy has been known as a material creating significant added value in various industrial fields based on its characteristics which cannot be easily obtained in other materials.
Elastic modulus difference between bones and conventional titanium alloys used as in vivo implants is very huge. Such huge difference frequently causes bone stress shielding that a low stress is applied in a bone structure having a relatively low elastic modulus. It makes the body system perceive the bone structure in which the low stress is applied as an unnecessary part, which activates osteoclasts and, therefore, dissolves the bone structure.
It is at present necessary to develop a low elastic modulus titanium alloy for use as an in vivo implant material in order to minimize the bone stress shielding phenomenon. Particularly, implants for orthopedic devices require not only low elastic modulus and high strength but also superelasticity and superplasticity giving good formability, since their forged shape is very complicated. It is therefore urgent to develop the titanium alloy meeting such requirements. The titanium alloy having such low elastic modulus, high strength, superelasticity, and superplasticity may be employed in various fields including aerospace, electricity generation, household items, and other industrial parts, as well in vivo implants. It may be also employed as injection mold materials for use under corrosion or other peculiar environments. Stainless steels, such as 316L type stainless steel, and cobalt alloys have been used as in vivo implant materials. However, those metals are implanted in a human body, they produce some problems as follows: first, metal ions are released in blood by in vivo corrosion, which spread all over the body along blood vessels and cause various diseases; second, when implants made of metals without bioactivity are inserted into the body, they are easily separated from the implanted parts over time after implanting; last, because the elastic modulus of such implants is so higher than that of the bone that the bone tissues around the implants are damaged due to the bone stress shielding, the implants become loose against the implanted parts and, therefore, reoperation is needed.
Researches to develop a titanium alloy with high bio-compatibility have been actively done in order to solve such problems. Specially, researchers have tried to obtain a titanium alloy with ultrahigh strength and ultralow elastic modulus, which cannot be obtained in conventional pure titanium metal and Ti-6Al-4V alloys. Because the titanium alloy with high strength and low elastic modulus can improve compatibility with bone tissues and avoid the bone stress shielding compared with prior alloys with high strength and high elastic modulus, researches about such a titanium alloy have been undertook at home and abroad.
U.S. Pat. No. 5,954,724 discloses a low modulus titanium alloy suitable for use in the construction of medical implants and devices, and U.S. Pat. No. 7,887,584 discloses medical devices containing at least one amorphous metal alloy. However, those patents only focus on development of a low elastic modulus titanium alloy, since the elastic modulus of conventional titanium alloys and other metals is higher than that of the bone. Until now, there is no success in developing a titanium alloy having improved mechanical and physical properties in addition to lower elastic modulus.